Setting the DDR of the serial pins before initializing the serial
hardware caused some logic '1' spikes on the tx line.

This was done because I was suspecting an error to be there. This is
not the case, so we probably have a Hardware Problem with our USB
Serial Stuff… If we send data too fast it sends garbage. It also always
sends two additional bytes (0xC2 at the beginning, 0xFF at the end),
which both come at the beginning if we don't delay between sending the
chars…